LONDON, Aug 8 (Reuters) - Robust U.S. earnings and expectations of additional stimulus from Beijing supported world shares at one-week highs on Wednesday but a selloff in Britain’s pound gathered steam over mounting concerns for the country’s outlook.

Equity futures suggested a modestly weaker open on Wall Street where the S&P 500 index closed Tuesday less than half a percent off record highs hit in January. That testifies to the strength of its economy and corporate sector, with average earnings expanding more than 23 percent in the second quarter.

The picture in the rest of the world is less rosy, given slower economic momentum and the greater vulnerability of other big economies - from China to Germany - to U.S. trade levies. Washington is preparing to start collecting tariffs on an additional $16 billion in Chinese goods.

While markets across Asia were broadly supported by the U.S. tech rally, MSCI’s index of stocks from 47 countries was just above flat.

“Everyone is just focusing on U.S. earnings...and feeling the U.S. market will remain robust despite trade uncertainties, and that’s the main driver right now,” said Christophe Barraud, a strategist at Paris-based brokerage Market Securities.

But Barraud said autumn could bring a reality check in the form of slower U.S. growth indicators, Italian politics, Britain’s Brexit talks, U.S. mid-term elections and - above all - the risk of a trade war escalation.

“Support from U.S. earnings could last until the end of August and when people are back in September they will focus more on other events,” he said.

Indeed, support from company earnings is less evident elsewhere — European shares slipped a touch and while average European second quarter earnings growth is at a relatively healthy 9.9 percent, according to Thomson Reuters I/B/E/S, the rate significantly lags Wall Street.

In other markets, Chinese equities fell 1.3 percent as news of the additional U.S. tariffs overshadowed strong trade data that showed exports rose more than expected in July. A rise in imports also suggested Chinese domestic demand remains resilient.

Trade fears were tempered somewhat by signs Beijing is unveiling further measures to support growth. That’s lifted the yuan off recent 15-month lows to the dollar though the currency weakened 0.3 percent on the day.

However, the biggest currency market moves of the day came on the British pound which tumbled to 11-month lows against the dollar and yen and a nine-month low against the euro.

Its woes stem from mounting concerns that Britain could crash out of the European Union without a trade deal in place, raising fears of a serious hit to the economy. That prompted the Bank of England last week to signal an extremely cautious trajectory for interest rate rises in the coming years.

Market players said investors were moving to hedge sterling risks.

“A lot of companies can’t wait until the (Brexit) outcome is clear ... Many of them are trying to hedge against a drop in sterling,” Barraud of Market Securities said.

Options markets indicated the currency heading for further weakness over nine-to-12 months - beyond the March 2019 date when the country is scheduled to leave the EU.

Elsewhere the Turkish lira, the biggest mover in recent days, fell another 1.5 percent to the dollar on fears of an economic crisis triggered by galloping inflation and worsening ties with the United States. The lira stayed off recent record lows however.

On oil markets, Brent futures held firm around $75 a barrel as U.S. sanctions on Iranian goods went into effect, intensifying concerns of looming crude supply shortages. Brent is up 2 percent this week.

Reporting by Sujata Rao in London, additional reporting by
Hideyuki Sano in Tokyo; editing by John Stonestreet, Richard
Balmforth